This invention relates to a fuel supply system for a direct injection type engine.
A fuel supply system has been disclosed, for example, in Japanese Application Patent Laid-open Publication No. Hei 11-294243, in which a system ever-changing fuel pressures are detected using sensors, an actual fuel injection rate of each fuel injection valve (hereinafter called an injector) is calculated from data sent from the sensors, and the fuel injection command value of each injector is corrected so as to match the actual fuel injection rate with a target fuel injection rate, thus evening off the fuel injection rates at each of the cylinders.
Further, Japanese Application Patent Laid-open Publication No. Hei 11-36935 discloses a system for obtaining a target fuel injection rate by extending the fuel injection time of an injector when the actual fuel pressure is lower than a target fuel pressure and shortening the fuel injection time of an injector when the actual fuel pressure is higher than a target fuel pressure.
A system is disclosed in Japanese Application Patent Laid-open Publication No. Hei 11-294243 in which it is necessary to fetch and calculate quickly changing fuel pressures at a high speed and output resulting signals to injectors. This increases the load on the controller. Each fuel injection by an injector is some milliseconds long, and the fuel pressure changes greatly also in some milliseconds. However, the controller usually requires in some milliseconds to 10 milliseconds to effect calculations. Therefore, it is difficult for the controller to precisely detect a quickly-changing fuel pressure. Further, it is assumed that an expensive controller is required to process such data at a high speed.
Finally, a system is disclosed in Japanese Application Patent Laid-open Publication No. Hei 11-36935 which uses only one pressure sensor to correct injection time periods of all injectors at one time from data obtained by the sensor. However, this technique cannot reduce the unevenness of injection rates of the injectors.
The primary object of the present invention is to provide a fuel supply system for an engine which can correct injection command values for respective injectors without using information based on ever-changing fuel pressures and reduce the unevenness of injection rates of the injectors.
The above object can be attained by a fuel supply system for a direct injection type engine comprising a fuel pump which supplies fuel to injection valves from a comparison chamber by varying the volume of the compression chamber by reciprocal movement of a single-cylinder plunger; a driving mechanism which produces one reciprocal movement of said plunger while said injection valves inject fuel into as many as two cylinders; and a controller which controls said fuel pump to adjust the fuel supply pressure, the injection start timing, and the injection time width of said fuel injection valve, wherein said controller operates to make the injection time width of one of said two fuel injection valves longer and that of the other fuel injection valve shorter.
The above object can also be attained by said fuel supply system, wherein said controller operates to detect the start timing and time width of intermittent fuel discharge that said high pressure fuel pump produces in synchronism with said plunger and to correct the fuel injection time width of each fuel injection valve relative to a target injection time width according to a time period during which the discharge period of said high-pressure fuel pump and the injection period of said fuel injection valve overlap with each other, the target injection time width of each fuel injection valve being calculated from the running status of said direct injection engine and the mean value of said fuel supply pressures.
The above object can also be attained by said fuel supply system, wherein said controller operates to compare the phase of the discharge time period of said high pressure fuel pump with the phase of the injection time period of said fuel injection valve, to determine whether to increase or decrease said fuel injection time width for correction, to determine a maximum injection time width to be corrected from said target fuel injection time width and the mean value of said fuel supply pressures, to subtract the correction time period to be given to each fuel injection valve according to the extent of overlapping between said discharge time period and said injection time period from said maximum fuel injection time width for correction, and to output the result.
The above object can also be attained by said fuel supply system, wherein said controller operates to detect an overlapping between the discharge time period of said high pressure fuel pump and the injection time period of said fuel injection valve. If there is no overlapping between them, the controller operates to shorten the injection time period of a first fuel injection valve that first injects fuel after one discharge by said high pressure fuel pump is completed and to extend the injection time period of a second fuel injection valve that injects fuel next; whereas, if there is an overlapping and if the high pressure fuel pump supplies about one fourth or less of the whole fuel discharge quantity by the injection start timing of the fuel injection valve, whose injection time period overlaps the discharge time period, the controller operates to extend the injection time period of the fuel injection valve whose injection time period overlaps the discharge time period and to shorten the injection time period of the other fuel injection valve; or, if the high pressure fuel pump supplies about one fourth or more of the whole fuel discharge quantity, the controller operates to shorten the injection time period of the fuel injection valve whose injection time period overlaps the discharge time period and to extend the injection time period of the other fuel injection valve.
The above object can also be attained by said fuel supply system, wherein said controller operates to detect a pressure of supplying fuel to said fuel injection valve, to extend the injection time width of a fuel injection valve whose fuel supply pressure is lower then a given value, and to shorten the injection time width of a fuel injection valve whose fuel supply pressure is higher than a given value.